The invention relates to an additive suitable in the manufacture of synthetic foam and in the manufacture of pressed wood boards or molded wood parts for a reduction of formaldehyde emission as well as for fire protection which additive is mixed with the base materials, that is, wood fibers or wood particles or other available lignocellular materials to which urea formaldehyde condensate or isocyanate glues are applied and which are then spread and then compressed in a hot press.
During the manufacture of fiber boards of medium density (MDF boards) as well as wood particle boards including flat-pressed boards as well as extrusion pressed boards or molded bodies, curable synthetic resin glues are used as adhesives, particularly urea formaldehyde condensates as well as melamine formaldehyde condensates. These synthetic resin glues are supplied as colloidal solutions which have dispersed therein particles of a size of 1/100,000 mm to 1/10,000,000 mm. Such a solution, termed a brine, contains, in addition to the solvent water, also urea or respectively, melamine formaldehyde condensates in which, however, the polycondensation reaction was interrupted. This interrupted polycondensation reaction is resumed during hot pressing of the particle boards while, at the same time, water is physically removed from the glue connections. The course and the speed of the chemical reaction of the glue particles, especially with urea formaldehyde condensate, are highly dependent on the pH-value. Adjustment of the pH value is performed by addition of a hardener providing for the needed acidic environment.
Besides the addition of hardener which is generally not necessary for melamine urea formaldehyde condensates, the chemical reaction of the condensate partner depends on the Mol ratio, which in connection with urea formaldehyde condensates should be about 1:2 (urea:formaldehyde) in order to achieve rapid condensation of the partners. Under such conditions, with careful maintenance of the desired Mol ratio, the temperature, time and pH value condition, first monomethylol and dimenthylol will form and then, by condensation with one another or with urea mixtures of condensation, products with ether connections or methylene connections are formed. Out of these still water soluble compounds branched and finally cross-linked condensates are formed during the reaction progressing under the heat application. In the water unsoluble cured urea formaldehyde condensation, the urea molecules are polymerized in a three-dimensional lattice structure which provides for high binding forces.
The above-indicated Mol ratio of 1:2 has the disadvantage that, after manufacturing of the panels, there is still free formaldehyde which is released slowly to the environment. This gas has a stinging odor which does not only detract from the use value of the boards manufactured from wooden material, in this manner, but if inhaled it can also cause poisoning. In order to at least limit the amount of formaldehyde remaining in the panel it was practice so far to reduce the Mol ratio down to a value of 1:1.08. With such a Mol ratio, only a very small amount of free formaldehyde remains in practice but such as small formaldehyde component amount in the urea formaldehyde resin glue does not only slow down the polycondensation process but also the formation of the above-referred to three-dimensional lattice structure and the strength of the glue. In practice one tries therefore to achieve a Mol ratio of 1:1.3 with which the amount of the free formaldehyde remaining in the particle board and slowly released therefrom can still be tolerated and which still provides for satisfactory strength. Further possibilities for the reduction of formaldehyde release which however are not or only to a small degree utilized in the industry are found for example in patent publications DOS 34 43 002 and 37 33 630 and EP-B 150 420.
It is accordingly the first object of the present invention to provide a procedure by which the amount of the formaldehyde remaining in wood material in spite of good manufacturing processes with mole ratios of 1:1.3 or higher and a correspondingly high strength of the final product may be minimized to such a degree that any formaldehyde release will no longer have any effects on the environment. Of course, this is not a problem for materials glued with isocyanate nor for resin foam materials.
For a large part of particle board applications as well as resin foam material applications, fire retardant or fire proofing provisions would be very suitable. Fire retardant particle boards in accordance with existing standards such as CSE RF 3/77, Class I for Italy, NFP 92/501M1 for France, BS 476, Part 7 Class 1 and BS 476, Part 6 Class 0 for Great Britain and DIN 4102 B1 for Germany, wherein fire protection is achieved by the addition of fire retardant materials, are basically known. In this connection reference is made to European patent application 03 51 670, EP-B 01 64 555 or German Patents 28 31 633 and 33 46 908. The fire extinguishing materials described therein are present in these cases almost exclusively in the form of salts, i.e., bromine and bromates, boron and borates, phosphates, sulfates and similar. These salts are commercially available in powder form with a powder particle size of maximally 50 my. All these methods and applications however are very uneconomical and reduce the strength of the finished product to some extent if they provide for some noticeable fire protection.
It is therefore the second object of the invention to provide a suitable fire protection compound which, as a result of its effective compound combination provides for effective fire protection but which does not adversely affect the properties of the resin material foams or those of the respective wood materials, especially not the gluing of the materials or their strength.